Mortgage Payment Calculator
Use this calculator to estimate your monthly mortgage payments. Understanding your potential monthly payment is a crucial step in the home-buying process.
Understanding Your Mortgage Payment
A mortgage is a long-term loan used to purchase real estate. The monthly payment for a fixed-rate mortgage is calculated using a standard formula that takes into account the principal loan amount, the interest rate, and the loan term.
The Mortgage Payment Formula
The formula for calculating the monthly mortgage payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
- P = Principal loan amount
- i = Monthly interest rate (Annual interest rate divided by 12)
- n = Total number of payments (Loan term in years multiplied by 12)
For example, if you borrow $200,000 at an annual interest rate of 4.5% for 30 years:
- P = $200,000
- Annual interest rate = 4.5% or 0.045
- Monthly interest rate (i) = 0.045 / 12 = 0.00375
- Loan term = 30 years
- Total number of payments (n) = 30 * 12 = 360
Plugging these values into the formula will give you your estimated monthly principal and interest payment. This calculator simplifies that process for you.
Important Note: This calculation typically only includes the principal and interest (P&I). Your actual monthly housing payment will likely be higher as it may include property taxes, homeowner's insurance, and potentially private mortgage insurance (PMI) or homeowner association (HOA) fees. These additional costs are often referred to as PITI (Principal, Interest, Taxes, and Insurance).
#mortgage-calculator-app {
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max-width: 600px;
margin: 20px auto;
padding: 20px;
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border-radius: 8px;
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.calculator-result {
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.calculator-explanation code {
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padding: 2px 5px;
border-radius: 3px;
font-family: Consolas, Monaco, 'Andale Mono', 'Ubuntu Mono', monospace;
}
function calculateMortgage() {
var principal = parseFloat(document.getElementById("loanAmount").value);
var annualRate = parseFloat(document.getElementById("annualInterestRate").value);
var years = parseFloat(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("mortgageResult");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(principal) || isNaN(annualRate) || isNaN(years) || principal <= 0 || annualRate < 0 || years <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
var monthlyRate = annualRate / 100 / 12;
var numberOfPayments = years * 12;
// Mortgage payment formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
var monthlyPayment = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
if (isNaN(monthlyPayment) || !isFinite(monthlyPayment)) {
resultDiv.innerHTML = "Calculation error. Please check your inputs.";
return;
}
resultDiv.innerHTML = "Estimated Monthly Payment:
$" + monthlyPayment.toFixed(2) + " (Principal & Interest)";
}